DNA damage induced by peroxynitrite: subsequent biological effects

Early inflammatory response to asbestos exposure in rat and hamster lungs: role of inducible nitric oxide synthase

Recent studies have suggested that inducible nitric oxide synthase (iNOS) plays a role in the development of asbestos-related pulmonary disorders. The pulmonary reactions of rats and hamsters upon exposure to asbestos fibers are well known to be disparate. In addition, in vitro experiments have indicated that mononuclear phagocytes from hamsters, in contrast to those from rats, lack the iNOS pathway. Therefore, the purpose of this study was to investigate whether rats and hamsters differ in lung iNOS expression in vivo upon exposure to asbestos fibers and whether differences in iNOS induction are associated with differences in the acute pulmonary inflammatory reaction. Body weight, alveolar-arterial oxygen difference, differential cell count in bronchoalveolar lavage fluid, total protein leakage, lung myeloperoxidase activity and lipidperoxidation, wet/dry ratio, iNOS mRNA and protein expression, and nitrotyrosine staining of lung tissue were determined 1 and 7 days after intratracheal instillation of asbestos fibers in CD rats and Syrian golden hamsters. Exposure of rats to asbestos fibers resulted in enhanced pulmonary iNOS expression and nitrotyrosine staining together with an acute inflammation that was characterized by an influx of neutrophils, enhanced myeloperoxidase activity and lipid peroxidation, damage of the alveolar-capillary membrane, edema formation, and impairment of gas exchange. In comparison, instillation of asbestos fibers in hamsters resulted in a significantly milder inflammatory reaction of the lung with no induction of iNOS in pulmonary cells. The data obtained provide important information to understand the underlying mechanisms of species differences in the pulmonary response upon exposure to asbestos fibers.

Serum uric acid levels in multiple sclerosis patients correlate with activity of disease and blood-brain barrier dysfunction

Several findings suggest lower levels of serum uric acid in multiple sclerosis (MS) patients. The aim of this study is to investigate relationships of uric acid serum levels in relapse-remitting (RR) MS patients with clinical activity of disease and blood-brain barrier (BBB) condition. Sixty-three definite RRMS patients and 40 controls divided into two groups: 20 healthy donors and 20 patients with other inflammatory neurological diseases (OINDs) were analysed. By using a quantitative enzymatic assay according to the manufacture's protocol and a commercial uric acid standard solution, serum uric acid levels were measured and the results were standardized. To investigate BBB function, magnetic resonance imaging after administration of gadolinium was used. MS patients were found to have significantly lower serum uric acid levels (193.89 +/- 49.05 micromol/l; mean value +/-SD) in comparison with healthy donors (292.7 +/- 58.65 micromol/l; P=0.000) and OIND patients (242.7 +/- 46.66 micromol/l; P=0.001). We found that MS patients with relapse had significantly lower serum uric acid levels (161.49 +/- 23.61 micromol/l) than MS patients with remission (234.39 +/- 41.96 micromol/l; P=0.000) and more over, MS patients with BBB disruption had significantly lower serum uric acid levels (163.95 +/- 26.07 micromol/l) than those with normal BBB (252.48 +/- 25.94 micromol/l; P=0.000). Further, we also found that serum uric acid level independently correlated with disease activity, BBB disruption, and gender. These results indicate that lower uric acid levels in MS patients are associated with relapse and suggest that uric acid might be beneficial in the treatment of MS.

Transcriptional activation of nitric oxide synthase-2, and NO-induced cell death, in mouse cerebrovascular endothelium exposed to Neisseria meningitidis

The site and mechanisms by which meningococci gain access to the CNS are unclear. In this study we determined whether production of nitric oxide (NO) is part of the host (endothelial cell) response to meningococcal cell lysate, and the consequences for endothelial cell viability. Expression of NO synthase type II (NOS-2) mRNA, protein and enzyme activity were investigated in mouse cerebrovascular endothelial cells exposed to sonicated Neisseria meningitidis. The production of nitrite peaked after 48 h of incubation, and this reflected transcriptional activation of the NOS-2 gene and increased expression of the NOS-2 protein. This endothelial response was independent of meningococcal lipopolysaccharide production. Endothelial cell death occurred as a result of NO production, and addition of a NOS inhibitor prevented cell death, but the cells did not exhibit features of apoptosis. However, inhibition of poly (ADP-ribose) polymerase (PARP) decreased the rate of cell death by more than 40%. These data indicate that N. meningitidis increases expression of NOS-2 in endothelial cells and causes cell death. Such an effect could contribute to meningococcal entry into the CNS in situ.

Poly(adenosine 5'-diphosphate) ribose polymerase activation as a cause of metabolic dysfunction in critical illness

Poly(adenosine 5'-diphosphate) ribose polymerase is a nuclear enzyme activated in response to genotoxic stress induced by a variety of DNA damaging agents. Several oxygen and nitrogen-centered free radicals, notably peroxynitrite, are strong inducers of DNA damage and poly(adenosine 5'-diphosphate) ribose polymerase activation in vitro and in vivo. Activation of this nuclear enzyme depletes the intracellular stores of its substrate nicotinamide adenine dinucleotide, slowing the rate of glycolysis, mitochondrial electron transport and adenosine triphosphate formation. This process triggers a severe energetic crisis within the cell, leading to acute cell dysfunction and cell necrosis. Poly(adenosine 5'-diphosphate) ribose polymerase also plays an important role in the regulation of inflammatory cascades, through a functional association with various transcription factors and transcription co-activators. Recent works identified this enzyme as a critical mediator of cellular metabolic dysfunction, inflammatory injury, and organ damage in conditions associated with overwhelming oxidative stress, including systemic inflammation, circulatory shock, and ischemia-reperfusion. Accordingly, pharmacological inhibitors of poly(adenosine 5'-diphosphate) ribose polymerase protect against cell death and tissue injury in such conditions, and may therefore represent novel therapeutic tools to limit multiple organ damage and dysfunction in critically ill patients.

Circadian variation in oxidative stress markers in healthy and type II diabetic men

Seven clinically healthy, nondiabetic (ND) and four Type II diabetic (D) men were assessed for circadian rhythms in oxidative "stress markers." Blood samples were collected at 3h intervals for approximately 27 h beginning at 19:00h. Urine samples were collected every 3 h beginning with the 16:00h-19:00h sample. The dark (sleep) phase of the light-dark cycle extended from 22:30h to 06:30h, with brief awakening for sampling at 01:00h and 04:00h. Subjects were offered general hospital meals at 16:30h, 07:30h, and 13:30h (2400 cal in total/24h). Serum samples were analyzed for uric acid (UA) and nitrite (NO) concentrations, and urine samples were assayed for 8-hydroxydeoxyguanosine (8-OHdG), malondialdehyde (MDA), and 8-isoprostane (ISP). Data were analyzed statistically both by the population multiple-components method and by the analysis of variance (ANOVA). The 24h mean level of UA and NO was greater in D than in ND subjects (424 vs. 338 micromol/L and 39.2 vs. 12.7 microM, respectively). A significant circadian rhythm in UA (p = 0.001) and NO (p = 0.048) was evident in ND but not in D (p = 0.214 and 0.065). A circadian rhythm (p = 0.004, amplitude = 8.6 pmol/kgbw/3h urine vol.) was also evident in urine 8-OHdG of ND but not of D. The 24h mean levels of ND and D were comparable (76.8 vs. 65.7 pmol/kgbw/3h urine vol.). No circadian rhythm by population multiple-components was evident in MDA and ISP levels of ND subjects, or in 8-OHdG, MDA, and ISP in D. However, a significant time-effect was demonstrated by ANOVA in all variables and groups. The 24h mean of MDA and ISP in D was significantly greater than in ND (214 vs. 119 nmol/3h urine vol. and 622 vs. 465 ng/3h urine vol.). The peak concentrations of the three oxidative "stress markers" in urine, like those of serum NO, occurred early in the evening in both groups of men. This observation suggests a correlation between increased oxidative damage and increased rate of anabolic-catabolic events as evidenced by similarities in the timing of peak NO production and in parameters relevant to metabolic functions.

3-Morpholinosydnonimine hydrochloride induces p53-dependent apoptosis in murine primary neural cells: a critical role for p21(ras)-MAPK-p19(ARF) pathway

In some neurological disorders, excessive nitric oxide (NO, nitrogen monoxide) produced by inducible and/or neuronal nitric oxide synthases (iNOS and nNOS) is able to combine with superoxide (O(minus sign)(2)) to form peroxynitrite (ONOO(minus sign)), which can then induce p53-dependent neural apoptosis. In the present study, experiments using p53 knock-out mice primary neural cells revealed that 3-morpholinosydnonimine hydrochloride (SIN-1), a peroxynitrite donor, triggered apoptosis, while p53-transcriptional activity was effectively suppressed in the absence of p53 molecules. This shows that SIN-1 was able to induce p53-dependent apoptosis in murine primary neural cells. The mechanism responsible for the SIN-1-induced accumulation of p53 molecules was then analyzed. Western blot analysis indicated that p53 accumulation caused by SIN-1 did not require p53 phosphorylation, whereas SIN-1 treatment triggered MAP kinase (MAPK) phosphorylation and pretreatment with the MAP kinase kinase (MEK) inhibitor U0126 inhibited p53 accumulation. Pretreatment of the neural cells with lovastatin, an inhibitor of p21(ras) signaling, greatly inhibited the accumulation of p53 induced by SIN-1. Northern blot and immunofluorescence analyses revealed that primary neural cells treated with SIN-1 had increased levels of p19 alternate reading frame (p19(ARF)) mRNA and protein, which is induced by MAPK and stabilizes the p53 protein. Our findings clearly show that the p21(ras)-MAPK-p19(ARF) pathway has an essential role in p53-dependent apoptosis triggered by peroxynitrite in neural cells.

Evidence of oxidative stress in human corneal diseases

This study localized malondialdehyde (MDA, a toxic byproduct of lipid peroxidation), nitrotyrosine [NT, a cytotoxic byproduct of nitric oxide (NO)], and nitric oxide synthase isomers (NOS) in normal and diseased human corneas. Normal corneas (n=11) and those with clinical and histopathological diagnoses of keratoconus (n=26), bullous keratopathy (n=17), and Fuchs' endothelial dystrophy (n=12) were examined with antibodies specific for MDA, NT, eNOS (constitutive NOS), and iNOS (inducible NOS). Normal corneas showed little or no staining for MDA, NT, or iNOS, whereas eNOS was detected in the epithelium and endothelium. MDA was present in all disease groups, with each group displaying a distinct pattern of staining. NT was detected in all keratoconus and approximately one half of Fuchs' dystrophy corneas. iNOS and eNOS were evident in all the diseased corneas. Keratoconus corneas showed evidence of oxidative damage from cytotoxic byproducts generated by lipid peroxidation and the NO pathway. Bullous keratopathy corneas displayed byproducts of lipid peroxidation but not peroxynitrite (MDA but not NT). Conversely, Fuchs' dystrophy corneas displayed byproducts of peroxynitrite with little lipid peroxidation (NT >> MDA). These data suggest that oxidative damage occurs within each group of diseased corneas. However, each disease exhibits a distinctive profile, with only keratoconus showing prominent staining for both nitrotyrosine and MDA. These results suggest that keratoconus corneas do not process reactive oxygen species in a normal manner, which may play a major role in the pathogenesis of this disease.

Mitochondrial reactive oxygen species in cell death signaling

During apoptosis, mitochondrial membrane permeability (MMP) increases and the release into the cytosol of pro-apoptotic factors (procaspases, caspase activators and caspase-independent factors such as apoptosis-inducing factor (AIF)) leads to the apoptotic phenotype. Apart from this pivotal role of mitochondria during the execution phase of apoptosis (documented in other reviews of this issue), it appears that reactive oxygen species (ROS) produced by the mitochondria can be involved in cell death. These toxic compounds are normally detoxified by the cells, failing which oxidative stress occurs. However, ROS are not only dangerous molecules for the cell, but they also display a physiological role, as mediators in signal transduction pathways. ROS participate in early and late steps of the regulation of apoptosis, according to different possible molecular mechanisms. In agreement with this role of ROS in apoptosis signaling, inhibition of apoptosis by anti-apoptotic Bcl-2 and Bcl-x(L) is associated with a protection against ROS and/or a shift of the cellular redox potential to a more reduced state. Furthermore, the fact that active forms of cell death in yeast and plants also involve ROS suggests the existence of an ancestral redox-sensitive death signaling pathway that has been independent of caspases and Bcl-2.

Oxides and apoptosis in inflammatory myopathies

Reactive oxygen intermediates (ROI) and nitric oxide (NO(.)) are produced in abundance in the inflammatory muscle diseases of autoimmune origin polymyositis (PM), dermatomyositis (DM), and inclusion body myositis (IBM). However, their role in the pathogenesis of these diseases is so far not clear. In contrast to demyelinating neuropathies, there is no convincing evidence for oxide-induced apoptosis either in myocytes or in lymphocytes and phagocytes in inflammatory myopathies. On the contrary, NO(.) released at low concentrations at target sites may even have cell-protective effects. A major mechanism of protection from apoptosis in both myocytes and inflammatory cells seems to be the upregulation of anti-apoptotic proteins like Bcl-2. Caution is warranted to apply antioxidative and anti-apoptotic agents to patients with inflammatory myopathies as long as the pathogenic role of oxides and apoptosis in the individual case is not resolved.

Complement-mediated cell death induced by rituximab in B-cell lymphoproliferative disorders is mediated in vitro by a caspase-independent mechanism involving the generation of reactive oxygen species

Mechanisms involving the in vitro effect of rituximab in cells from 55 patients with B-cell lymphoproliferative disorders were investigated. No cytotoxic effect was observed when cells were incubated with rituximab alone, but in the presence of human AB serum rituximab induced complement-dependent cell death (R-CDC). A cytotoxic effect was observed in cells from 9 of 33 patients with B-cell chronic lymphocytic leukemia, 16 of 16 patients with mantle-cell lymphoma, 4 of 4 patients with follicular lymphoma, and 2 of 2 patients with hairy-cell leukemia. R-CDC was observed in cells from patients expressing more than 50 x 10(3) CD20 molecules per cell, and directly correlated with the number of CD20 molecules per cell. Preincubation with anti-CD59 increased the cytotoxic effect of rituximab and sensitized cells from nonsensitive cases. Neither cleavage of poly-ADP ribose polymerase (PARP) nor activation of caspase-3 was observed in R-CDC. In addition, no cells with a hypodiploid DNA content were detected and R-CDC was not prevented by a broad-spectrum caspase inhibitor, suggesting a caspase-independent mechanism. Incubation with rituximab in the presence of AB serum induced a rapid and intense production of reactive oxygen species (ROS). R-CDC was blocked by the incubation of cells with N-acetyl-L-cysteine (NAC) or Tiron, 2 ROS scavengers, indicating that the cytotoxic effect was due to the generation of superoxide (O) radicals. In conclusion, the results of the present study suggest that CD20, CD59, and complement have a role in the in vitro cytotoxic effect of rituximab, which is mediated by a caspase-independent process that involves ROS generation.

Different effects of tert-butylhydroperoxide-induced peroxynitrite-dependent and -independent DNA single-strand breakage on PC12 cell poly(ADP-ribose) polymerase activity

The short-chain lipid hydroperoxide analogue tert-butylhydroperoxide induces peroxynitrite-dependent and -independent DNA single strand breakage in PC12 cells. U937 cells that do not express constitutive nitric oxide synthase respond to tert-butylhydroperoxide treatment with peroxynitrite-independent DNA cleavage. Under experimental conditions leading to equivalent strand break frequencies, the analysis of poly(ADP-ribose) polymerase activity showed an increase in PC12 cells but not in U937 cells. The enhanced poly(ADP-ribose) polymerase activity observed in PC12 cells was paralleled by a significant decline in NAD+ content and both events were prevented by treatments suppressing formation of peroxynitrite. Although DNA breaks were rejoined at similar rates in the two cell lines, an inhibitor of poly(ADP-ribose) polymerase delayed DNA repair in PC12 cells but had hardly any effect in U937 cells. The results obtained using the latter cell type were confirmed with an additional cell line (Chinese hamster ovary cells) that does not express nitric oxide synthase. Collectively, our data suggest that tert-butylhydroperoxide-induced peroxynitrite-independent DNA strand scission is far less effective than the DNA cleavage generated by endogenous peroxynitrite in stimulating the activity of poly(ADP-ribose) polymerase.

Is nitric oxide overproduction the target of choice for the management of septic shock?

Sepsis is a heterogeneous class of syndromes caused by a systemic inflammatory response to infection. Septic shock, a severe form of sepsis, is associated with the development of progressive damage in multiple organs, and is a leading cause of patient mortality in intensive care units. Despite important advances in understanding its pathophysiology, therapy remains largely symptomatic and supportive. A decade ago, the overproduction of nitric oxide (NO) had been discovered as a potentially important event in this condition. As a result, great hopes arose that the pharmacological inhibition of NO synthesis could be developed into an efficient, mechanism-based therapeutic approach. Since then, an extraordinary effort by the scientific community has brought a deeper insight regarding the feasibility of this goal. Here we present in summary form the present state of knowledge of the biological chemistry and physiology of NO. We then proceed to a systematic review of experimental and clinical data, indicating an up-regulation of NO production in septic shock; information on the role of NO in septic shock, as provided by experiments in transgenic mice that lack the ability to up-regulate NO production; effects of pharmacological inhibitors of NO production in various experimental models of septic shock; and relevant clinical experience. The accrued evidence suggests that the contribution of NO to the pathophysiology of septic shock is highly heterogeneous and, therefore, difficult to target therapeutically without appropriate monitoring tools, which do not exist at present.

Nitric oxide in gastrointestinal epithelial cell carcinogenesis: linking inflammation to oncogenesis

Chronic inflammation of gastrointestinal tissues is a well-recognized risk factor for the development of epithelial cell-derived malignancies. Although the inflammatory mediators linking chronic inflammation to carcinogenesis are numerous, current information suggests that nitric oxide (NO) contributes to carcinogenesis during chronic inflammation. Inducible nitric oxide synthase (iNOS), expressed by both macrophages and epithelial cells during inflammation, generates the bioreactive molecule NO. In addition to causing DNA lesions, NO can directly interact with proteins by nitrosylation and nitosation reactions. The consequences of protein damage by NO appear to be procarcinogenic. For example, NO inhibits DNA repair enzymes such as human 8-oxodeoxyguanosine DNA glycosylase 1 and blocks apoptosis via nitrosylation of caspases. These cellular events permit DNA damage to accumulate, which is required for the numerous mutations necessary for development of invasive cancer. NO also promotes cancer progression by functioning as an angiogenesis factor. Strategies to inhibit NO generation during chronic inflammation or to scavenge reactive nitrogen species may prove useful in decreasing the risk of cancer development in chronic inflammatory gastrointestinal diseases.

Molecular mechanisms underlying chemopreventive activities of anti-inflammatory phytochemicals: down-regulation of COX-2 and iNOS through suppression of NF-kappa B activation

A wide array of phenolic substances, particularly those present in edible and medicinal plants, have been reported to possess substantial anticarcinogenic and antimutagenic activities. The majority of naturally occurring phenolics retain antioxidative and anti-inflammatory properties which appear to contribute to their chemopreventive or chemoprotective activity. Cyclooxygenase-2 (COX-2) inducible and nitric oxide synthase (iNOS) are important enzymes that mediate inflammatory processes. Improper up-regulation of COX-2 and/or iNOS has been associated with pathophysiology of certain types of human cancers as well as inflammatory disorders. Since inflammation is closely linked to tumor promotion, substances with potent anti-inflammatory activities are anticipated to exert chemopreventive effects on carcinogenesis, particularly in the promotion stage. Examples are curcumin, a yellow pigment of turmeric (Curcuma longa L., Zingiberaceae), the green tea polyphenol epigallocatechin gallate (EGCG), and resveratrol from grapes (Vitis vinifera, Vitaceae) that strongly suppress tumor promotion. Recent studies have demonstrated that eukaryotic transcription factor nuclear factor-kappa B (NF-kappa B) is involved in regulation of COX-2 and iNOS expression. Several chemopreventive phytochemicals have been shown to inhibit COX-2 and iNOS expression by blocking improper NF-kappa B activation. Multiple lines of compelling evidence indicate that extracellular-regulated protein kinase and p38 mitogen-activated protein kinase are key elements of the intracellular signaling cascades responsible for NF-kappa B activation in response to a wide array of external stimuli. Curcumin, EGCG and resveratrol have been shown to suppress activation of NF-kappa B. One of the plausible mechanisms underlying inhibition of NF-kappa B activation by aforementioned phytochemicals involves repression of degradation of the inhibitory unit I kappa B alpha, which hampers subsequent nuclear translocation of the functionally active subunit of NF-kappa B.

Nitric oxide and reactive nitrogen intermediates during lethal and nonlethal strains of murine malaria

The virulence of Plasmodia depends partly on the strain of parasite and partly on the host. In this study, Plasmodium berghei N/13/1A/4/203 caused the death of mice, whereas Plasmodium chabaudi chabaudi AS was not lethal. Current opinion is that nitric oxide (NO) and other reactive nitrogen intermediates (RNI) are produced in several host organs during malaria to resist infection or produce tissue damage. NO and RNI production in blood or plasma, brain, liver and spleen in MF1 mice was investigated during P. berghei and P. c. chabaudi infection, in order to help determine whether changes in NO production are beneficial or detrimental to the host in vivo. NO production was measured both directly and indirectly as nitrites and nitrates, to represent RNI. No changes in blood NO were detected in P. berghei infected mice, but increases were observed in brain, liver and spleen. In P. c. chabaudi infected mice, rises in NO concentration were observed in blood and spleen, whereas a decline in liver NO was seen, but there were no changes in brain. Liver contained the highest concentration of RNI, but increasing concentrations were seen in both plasma and spleen in both P. berghei and P. c. chabaudi infected mice. These results show that NO and RNI production alters during murine malaria. The changes depend upon the tissue, the day of infection, the degree of parasitaemia, the strain of Plasmodia and the method of measuring NO biosynthesis. Lethal P. berghei induced NO production in the mid and late stages of infection in mice when parasitaemia was high, whereas in nonlethal P. c. chabaudi infection, NO production was increased in the early and late stages when parasitaemia was low. These data are consistent with a role for NO in the protection of the MF1 mouse against Plasmodia. Failure to clear the parasite is associated with evidence of increased NO production in brain and liver, which may contribute to the pathology of malaria, but this hypothesis requires confirmation from other experimental approaches.

S-nitrosothiols do not induce oxidative stress, contrary to other nitric oxide donors, in cultures of vascular endothelial or smooth muscle cells

Nitric oxide (NO) has been described to exert various anti-atherogenic actions. However, NO, in some cases, has been shown to stimulate the oxidation of low-density lipoprotein (LDL), which constitute an important triggering event in atherosclerosis. Thus, some NO donors, despite their advantages, might also induce oxidative stress. Therefore, the purpose of this study is to examine the effect of three different NO donors on LDL oxidation, in acellular system as well as in cultures of normal endothelial cells or smooth muscle cells, which constitute the two major cellular components of the arterial wall. Sodium nitroprusside oxidized strongly LDL in medium alone as well as in endothelial or smooth muscle cell cultures. Sydnonimine-1 (SIN-1) oxidized LDL already in the absence of cells and enhanced clearly the LDL oxidation in the cultures. S-nitroso-N-acetylpenicillamine was unable to oxidize LDL in synthetic medium alone as well as in the presence of cells, showing that the amount of superoxide and other reactive oxygen species released by these cells did not suffice, contrary to those liberated by macrophages, to combine to NO providing oxidant activity.

The regulatory role of nitric oxide in apoptosis

Nitric oxide (NO) is a multi-faceted molecule with dichotomous regulatory roles in many areas of biology. The complexity of its biological effects is a consequence of its numerous potential interactions with other molecules such as reactive oxygen species (ROS), metal ions, and proteins. The effects of NO are modulated by both direct and indirect interactions that can be dose-dependent and cell-type specific. For example, in some cell types NO can promote apoptosis, whereas in other cells NO inhibits apoptosis. In hepatocytes, NO can inhibit the main mediators of cell death-caspase proteases. Moreover, low physiological concentrations of NO can inhibit apoptosis, but higher concentrations of NO may be toxic. High NO concentrations lead to the formation of toxic reaction products like dinitrogen trioxide or peroxynitrite that induce cell death, if not by apoptosis, then by necrosis. Long-term exposure to nitric oxide in certain conditions like chronic inflammatory states may predispose cells to tumorigenesis through DNA damage, inhibition of DNA repair, alteration in programmed cell death, or activation of proliferative signaling pathways. Understanding the regulatory mechanisms of NO in apoptosis and carcinogenesis will provide important clues to the diagnosis and treatment of tissue damage and cancer. In this article we have reviewed recent discoveries in the regulatory role of NO in specific cell types, mechanisms of pro-apoptotic and anti-apoptotic induction by NO, and insights into the effects of NO on tumor biology.

Intracellular ascorbic acid enhances the DNA single-strand breakage and toxicity induced by peroxynitrite in U937 cells

A well-established protocol to increase the intracellular content of ascorbic acid was used to investigate the effects of the vitamin on DNA single-strand breakage and toxicity mediated by authentic peroxynitrite (ONOO(-)) in U937 cells. This protocol involved exposure for 60 min to 100 microM dehydroascorbic acid, which was taken up by the cells and converted into ascorbic acid via a GSH-independent mechanism. At the time of exposure to ONOO(-), which was performed in fresh saline immediately after loading with dehydroascorbic acid, the vitamin present in the cells was all in its reduced form. It was found that, in cells that are otherwise ascorbate-deficient, an increase in their ascorbic acid content does not prevent, but rather enhances, the DNA-damaging and lethal responses mediated by exogenous ONOO(-). These results therefore suggest that acute supplementation of ascorbic acid can be detrimental for individuals with pathologies associated with a decrease in ascorbic acid and in which ONOO(-) is known to promote deleterious effects.

Nitric oxide and Coxsackievirus B3 myocarditis: differential expression of inducible nitric oxide synthase in mouse heart after infection with virulent or attenuated virus

Increased expression of inducible nitric oxide synthase (iNOS) has been found in inflammatory myocardial disease and increased production of nitric oxide (NO) has both an inhibitory effect on virus replication and a cytotoxic effect on host cells. To investigate the relationship between severity of enteroviral myocarditis and iNOS expression, a characterised murine model was infected with either cardiovirulent or an attenuated Coxsackievirus B3 and myocardial samples were collected on Day 7. The ability of these viruses to induce NOS expression was compared by measurement of iNOS enzyme activity and localisation of iNOS protein or peroxynitrite, a product of excessive NO production. In accordance with previous reports, high expression of iNOS was detected in mice infected with the cardiovirulent virus. The iNOS protein was located mainly in infiltrating macrophages in and around foci of necrotic myofibres where viral genomic RNA was detected. In contrast, the level of iNOS expression was significantly lower in mice infected with the attenuated virus. This correlates with fewer and smaller myocarditic lesions and less infiltrating cells in the heart. iNOS was not detected in mock-infected mice by the above assays. These findings suggest that one mechanism of attenuation may be associated with the reduced ability of the variant to induce NOS expression in the heart. This also confirms a cytotoxic role for NO in the pathogenesis of Coxsackievirus B3-induced myocarditis.

Novel effects of nitric oxide

Nitric oxide (NO), a simple free radical gas, elicits a surprisingly wide range of physiological and pathophysiological effects. NO interacts with soluble guanylate cyclase to evoke many of these effects. However, NO can also interact with molecular oxygen and superoxide radicals to produce reactive nitrogen species that can modify a number of macromolecules including proteins, lipids, and nucleic acids. NO can also interact directly with transition metals. Here, we have reviewed the non--3',5'-cyclic-guanosine-monophosphate-mediated effects of NO including modifications of proteins, lipids, and nucleic acids.

Site-Selective Nitration of Tyrosine in Human Serum Albumin by Peroxynitrite

Peroxynitrite, which is formed in biological systems by the reaction of nitric oxide with superoxide anion, is a highly reactive molecule that can lead to cell injury or cell death. Reactions of peroxynitrite under physiological conditions include nitration of tyrosine-containing proteins or peptides, and we have been investigating the behavior of human serum albumin following exposure to peroxynitrite. Peroxynitrite, at relative concentrations ranging from 0.2 to 50 with respect to protein, was added to human serum albumin in buffer at pH 7.2. The resulting mixtures were dialyzed to remove small molecules, dried under vacuum, and then digested with trypsin. The digests were analyzed by high performance liquid chromatography with UV detection at 230 and 354 nm, the latter wavelength being selective for nitrotyrosine. At the higher relative concentrations of peroxynitrite, the 354-nm chromatograms contained a large number of peaks, including at least nine with molecular weights corresponding to nitration of nominal tryptic peptides. Following treatment with the lower relative concentrations of peroxynitrite, however, the 354-nm chromatograms were dominated by only two nitrated peptides; these were identified by comparison of LC retention times and collision-induced decomposition mass spectra as nitro-Y(411)TK(413) and nitro-Y(138)LYEIAR(144). Each of these tyrosines resides in a known reactive site within the protein, i.e., subdomains IIIA and IB, respectively.

Bi-directional effects of the elevation of intracellular calcium on the expression of inducible nitric oxide synthase in J774 macrophages exposed to low and to high concentrations of endotoxin

Nitric oxide produced through the action of inducible nitric oxide synthase (iNOS) is an important mediator in immune responses of the host. Various extracellular factors, including inflammatory stimuli, affect intracellular free Ca2+ levels ([Ca2+](i)), modulating cellular signalling and gene expression. In the present study we investigated the effects of increased ([Ca2+](i)) on NO production through the iNOS pathway in J774 macrophages. Thapsigargin (TG), a Ca2+-ATPase inhibitor, and the Ca2+ ionophore A23187 were used as tools to induce an increase in ([Ca2+](i)) in the cytosol. This increase was confirmed by the fura 2 method. The production of NO was measured as accumulated nitrite in the cell culture medium; iNOS protein and iNOS mRNA were detected by Western blotting and reverse-transcriptase-mediated PCR respectively. The activation of nuclear factor kappaB (NF-kappaB) was investigated by electrophoretic mobility-shift assay. TG (100 nM) induced a marked synthesis of iNOS mRNA, iNOS protein and NO in cells primed with a low concentration of endotoxin [lipopolysaccharide (LPS) 1 ng/ml], which on its own induced barely detectable NO synthesis. Stimulation by a high concentration of LPS (100 ng/ml) induced a marked expression of iNOS and NO production. Under these conditions, treatment with TG hindered the synthesis of iNOS protein and NO production by accelerating the degradation of iNOS mRNA. Treatment with TG (100 nM) did not affect the NF-kappaB activity induced by low (1 ng/ml) or high (100 ng/ml) concentrations of LPS. Viability of the cells was confirmed by the 2,3-bis[2-methoxy-4-nitro-5-sulphophenyl]-2H-tetrazolium-5-carboxyaniline ("XTT") method; apoptosis was ruled out by propidium iodide staining and flow cytometry. A23187 (1 microM) also transiently increased ([Ca2+](i)) and had opposite effects on NO production depending on the LPS concentration. Our results show that increased ([Ca2+](i)) induced the stimulation or suppression of NO production through iNOS in macrophages depending on the state of cell activation. These findings suggest that the receptor-mediated increase in ([Ca2+](i)) might be an important factor in the control of the balance between the up-regulation and down-regulation of inflammatory genes, including that encoding iNOS, depending on the phase of the inflammatory response.

Motor neurons rapidly accumulate DNA single-strand breaks after in vitro exposure to nitric oxide and peroxynitrite and in vivo axotomy

The mechanisms of neuronal degeneration in motor neuron disease are not fully understood. We tested the hypothesis that oxidative stress in vitro and axotomy in vivo induce single-strand breaks (SSB) in DNA, a form of early DNA damage, in adult motor neurons early during their degeneration. We developed and characterized a novel cell suspension system enriched in motor neurons from adult rat spinal cord ventral horn. This cell system is approximately 84% neurons, with approximately 86% of these neurons being motor neurons; approximately 72% of these motor neurons are alpha-motor neurons. Motor neuron viability in suspension is approximately 100% immediately after isolation and approximately 61% after 12 hours of incubation. During incubation, isolated motor neurons generate high levels of superoxide. We used single-cell gel electrophoresis (comet assay) to detect DNA-SSB in motor neurons. Exposure of motor neurons to nitric oxide (NO) donors (sodium nitroprusside or NONOate), H2O2, or NO donor plus H2O2 rapidly induces DNA-SSB and causes motor neuron degeneration, the occurrence of which is dose and time related, as represented by comet formation and cell loss. Motor neuron toxicity is potentiated by cotreatment with NO donor and H2O2 (at nontoxic concentrations alone). Peroxynitrite causes DNA-SSB in motor neurons. The DNA damage profiles (shown by the comet morphology and moment) of NO donors, NO donor plus H2O2, and peroxynitrite are similar. In an in vivo model of motor neuron apoptosis, DNA-SSB accumulate slowly in avulsed motor neurons before apoptotic nuclear features emerge, and the comet fingerprint is similar to NO toxicity. We conclude that motor neurons challenged by oxidative stress and axotomy accumulate DNA-SSB early in their degeneration and that the formation of peroxynitrite is involved in the mechanisms.

Nitric oxide disrupts H2O2-dependent activation of nuclear factor kappa B. Role in sensitization of human tumor cells to tumor necrosis factor-alpha -induced cytotoxicity

Tumor necrosis factor alpha (TNF-alpha) exerts its effect by two distinct signaling pathways. It can trigger cytotoxicity in sensitive target cells. TNF-alpha can also promote nuclear factor kappaB (NF-kappaB) activity and regulate the expression of genes that interfere with apoptosis and thus conferring resistance to several apoptotic stimuli. We have observed that interferon-gamma (IFN-gamma) sensitizes human ovarian carcinoma cell lines to TNF-alpha-mediated apoptosis and further, IFN-gamma induces the expression of the inducible nitric-oxide synthase (iNOS) and the generation of nitric oxide (NO). This study examines the role of NO in the sensitization of the ovarian carcinoma cell line AD10 to TNF-alpha-mediated cytotoxicity. Treatment of AD10 cells with the NOS inhibitor l-NMA blocked the IFN-gamma-dependent sensitization whereas NO donors (S-nitroso-N-acetylpenicillamine) sensitized these cells to TNF-alpha cytotoxicity. Analysis of the activation status of NF-kappaB upon treatment with NO donors confirmed the inhibitory role of NO on both the NF-kappaB DNA-binding property and its activation. Moreover, the inhibition of NF-kappaB nuclear translocation by NO donors directly correlated with the intracellular concentration of H(2)O(2) and was reversed by the addition of exogenous H(2)O(2). These findings show that NO might interfere with TNF-alpha-dependent NF-kappaB activation by interacting with O(2) and reducing the generation of H(2)O(2), a potent NF-kappaB activator. Therefore, NO-mediated disruption of NF-kappaB activation results in the removal of anti-apoptotic/resistance signals and sensitizes tumor cells to cytotoxic cytokines like TNF-alpha.

SIN-1-induced DNA damage in isolated human peripheral blood lymphocytes as assessed by single cell gel electrophoresis (comet assay)

Human lymphocytes were exposed to increasing concentrations of SIN-1, which generates superoxide and nitric oxide, and the formation of single-strand breaks (SSB) in individual cells was determined by the single-cell gel electrophoresis assay (comet assay). A dose- and time-dependent increase in SSB formation was observed rapidly after the addition of SIN-1 (0.1-15 mM). Exposure of the cells to SIN-1 (5 mM) in the presence of excess of superoxide dismutase (0.375 mM) increased the formation of SSB significantly, whereas 1000 U/ml catalase significantly decreased the quantity of SSB. The simultaneous presence of both superoxide dismutase and catalase before the addition of SIN-1 brought the level of SSB to that of the untreated cells. Moreover, pretreatment of the cells with the intracellular Ca(2+)-chelator BAPTA/AM inhibited SIN-1-induced DNA damage, indicating the involvement of intracellular Ca(2+) changes in this process. On the other hand, pretreatment of the same cells with ascorbate or dehydroascorbate did not offer any significant protection in this system. The data suggest that H2O2-induced changes in Ca(2+) homeostasis are the predominant pathway for the induction of SSB in human lymphocytes exposed to oxidants.

Bi-directional effects of the elevation of intracellular calcium on the expression of inducible nitric oxide synthase in J774 macrophages exposed to low and to high concentrations of endotoxin

Nitric oxide produced through the action of inducible nitric oxide synthase (iNOS) is an important mediator in immune responses of the host. Various extracellular factors, including inflammatory stimuli, affect intracellular free Ca2+ levels ([Ca2+](i)), modulating cellular signalling and gene expression. In the present study we investigated the effects of increased ([Ca2+](i)) on NO production through the iNOS pathway in J774 macrophages. Thapsigargin (TG), a Ca2+-ATPase inhibitor, and the Ca2+ ionophore A23187 were used as tools to induce an increase in ([Ca2+](i)) in the cytosol. This increase was confirmed by the fura 2 method. The production of NO was measured as accumulated nitrite in the cell culture medium; iNOS protein and iNOS mRNA were detected by Western blotting and reverse-transcriptase-mediated PCR respectively. The activation of nuclear factor kappaB (NF-kappaB) was investigated by electrophoretic mobility-shift assay. TG (100 nM) induced a marked synthesis of iNOS mRNA, iNOS protein and NO in cells primed with a low concentration of endotoxin [lipopolysaccharide (LPS) 1 ng/ml], which on its own induced barely detectable NO synthesis. Stimulation by a high concentration of LPS (100 ng/ml) induced a marked expression of iNOS and NO production. Under these conditions, treatment with TG hindered the synthesis of iNOS protein and NO production by accelerating the degradation of iNOS mRNA. Treatment with TG (100 nM) did not affect the NF-kappaB activity induced by low (1 ng/ml) or high (100 ng/ml) concentrations of LPS. Viability of the cells was confirmed by the 2,3-bis[2-methoxy-4-nitro-5-sulphophenyl]-2H-tetrazolium-5-carboxyaniline ("XTT") method; apoptosis was ruled out by propidium iodide staining and flow cytometry. A23187 (1 microM) also transiently increased ([Ca2+](i)) and had opposite effects on NO production depending on the LPS concentration. Our results show that increased ([Ca2+](i)) induced the stimulation or suppression of NO production through iNOS in macrophages depending on the state of cell activation. These findings suggest that the receptor-mediated increase in ([Ca2+](i)) might be an important factor in the control of the balance between the up-regulation and down-regulation of inflammatory genes, including that encoding iNOS, depending on the phase of the inflammatory response.

Role of free radicals in viral pathogenesis and mutation

Oxygen radicals and nitric oxide (NO) are generated in excess in a diverse array of microbial infections. Emerging concepts in free radical biology are now shedding light on the pathogenesis of various diseases. Free-radical induced pathogenicity in virus infections is of great importance, because evidence suggests that NO and oxygen radicals such as superoxide are key molecules in the pathogenesis of various infectious diseases. Although oxygen radicals and NO have an antimicrobial effect on bacteria and protozoa, they have opposing effects in virus infections such as influenza virus pneumonia and several other neurotropic virus infections. A high output of NO from inducible NO synthase, occurring in a variety of virus infections, produces highly reactive nitrogen oxide species, such as peroxynitrite, via interaction with oxygen radicals and reactive oxygen intermediates. The production of these various reactive species confers the diverse biological functions of NO. The reactive nitrogen species cause oxidative tissue injury and mutagenesis through oxidation and nitration of various biomolecules. The unique biological properties of free radicals are further illustrated by recent evidence showing accelerated viral mutation by NO-induced oxidative stress. NO appears to affect a host's immune response, with immunopathological consequences. For example, NO is reported to suppress type 1 helper T cell-dependent immune responses during infections, leading to type 2 helper T cell-biased immunological host responses. NO-induced immunosuppression may thus contribute to the pathogenesis of virus infections and help expansion of quasispecies population of viral pathogens. This review describes the pathophysiological roles of free radicals in the pathogenesis of viral disease and in viral mutation as related to both nonspecific inflammatory responses and immunological host reactions modulated by NO.

Rapid recovery and identification of anthrax bacteria from the environment

Bacillus anthracis has been recognized as a highly likely biological warfare or terrorist agent. We have designed culture techniques to rapidly isolate and identify "live" anthrax from suspected environmental release. A special medium (3AT medium) allows for discrimination between closely related bacilli and non-pathogenic strains. Nitrate was found to be a primary factor influencing spore formation in Bacillus anthracis. Nitrate reduction in anthrax is not an adaptation to saprophytic environmental existence, but it is a signal to enhance environmental survival upon the death of the anthrax host, which can be mimicked in culture.

"Malgun" (clear) cell change of gastric epithelium in chronic Helicobacter pylori gastritis

To characterize the Helicobacter pylori gastritis-associated epithelial change, we analyzed 251 randomly selected gastric biopsies. The "malgun" (clear) cell change of the gastric epithelium was noted in 229 biopsies (91.2%). Malgun cells were characterized by large, pale nuclei with a euchromatin pattern, enlarged nucleoli, and clear cytoplasm. In the proliferative zone, individual malgun cells and small clusters were often in close contact with infiltrating neutrophils, suggesting that they had developed individually in the background of acute foveolitis. Mitotic figures of malgun cells were not infrequent, including atypical ones. In the surface epithelium, most malgun cells were in clusters that were often large enough to occupy wide epithelial segments. With Warthin-Starry triple staining, they were distinguished by the absence of silver impregnation, while other cells showed staining of the heterochromatin. They displayed prominent immunostaining for low molecular weight cytokeratin (No. 8). Most malgun cells were PCNA-positive in both surface and proliferative zones, whereas Ki67-positive cells were found only in the proliferative zone. It was suggested that a population of malgun cells, which were positive for PCNA only, were in the process of active DNA repair. The malgun cell change may represent a "cellular pattern of activation" in a population which had significant DNA damage, but somehow escaped the detection by the apoptosis system. The notion of "damage at the genetic level" was supported by the observation that these cells remained at least for 8 weeks after eradication of the H. pylori infection.

Intervention du monoxyde d'azote, NO, et de ses dérivés oxydés, particulièrement chez les mammifères

Nitric oxide (NO) is a natural and stable free radical produced in soil and water by the bacteriological reduction of nitrites and nitrates and in animals by the enzyme oxidation of L-arginine. NO is biosynthesised by finely regulated enzymatic systems called NO-synthases and readily diffuses through tissues. It reacts rapidly with hemoproteins and iron-sulphur centers to form nitrosylated compounds. It oxidises more slowly to form nitrogen oxides that nitrosate thiols into thionitrite. NO is transported in these various forms and released spontaneously or through yet unclear mechanisms into most cells; it also regulates oxygen consumption at the mitochondrial respiratory chain level through interaction with cytochrome oxidase. In the cardiovascular system, NO lowers blood pressure by activating a hemoprotein, the guanylate cyclase present in muscle cells; through such interaction it acts also as a neuromediator and neuromodulator in the nervous system. However, many of NO's roles result from rapid coupling to other radicals; for example, it reacts with the superoxide anion (O–2) to form oxoperoxinitrate (ONOO–, also known as peroxynitrite). This strong oxidant of metallic centers, thiols, and antioxidants is also able to convert tyrosine to 3-nitrotyrosine and to act upon tyrosine residues contained in proteins. The biological aspects of the roles of NO are presented with particular respect to the rapid interactions of NO with hemoproteins' iron and other radicals. Concurrently, NO oxidation enables nitrosation reactions primarily of thiols but ultimately of nucleic bases. The thionitrite function (R-S-NO) thus formed and the dimerisation and nitration of tyrosine residues are protein post-translational modifications that are being investigated in animals.Key words: nitric oxide, peroxynitrite, nitration, nitrosation, nitrosylation. [Translated by the editors.]

Mechanisms of nitric oxide-induced cytotoxicity in normal human hepatocytes

Chronic exposure of hepatocytes to reactive nitrogen species (RNS) following liver injury and inflammation leads not only to functional and morphological alterations in the liver but also to degenerative liver diseases and hepatocellular carcinoma. Previously, we showed that S-nitroso-N-acetylpenicillamine-amine (SNAP), which generates nitric oxide, and 3-morpholinosydnonimine (Sin-1), which generates equal molar concentrations of superoxide and nitric oxide resulting in peroxynitrite production, exhibited different levels of cytotoxicity to normal human hepatocytes in culture. The aim of the present study was to elucidate some of the molecular and cellular pathways leading to hepatocyte cell death induced by RNS. Following treatment of the hepatocytes with SNAP or Sin-1, gene-specific DNA damage was measured in mtDNA and a hprt gene fragment using a quantitative Southern blot analysis. Both agents induced dose-dependent increases in DNA damage that was alkaline labile, but not sensitive to both formamidopyrimidine-DNA glycosylase (fpg) and endonuclease III, which recognize 8-oxoguanine, thymine glycol, and other oxidized pyrimidines. DNA damage was two- to fivefold greater in mtDNA than in the hprt gene fragment. There was a persistent and marked increase in DNA damage posttreatment that appeared to arise from the disruption of electron transport in the mitochondria, generating reactive species that saturated the repair system. DNA damage induced by Sin-1 and SNAP led to cell-cycle arrest in the S-phase, growth inhibition, and apoptosis. The data support the hypothesis that the functional and morphological changes observed in liver following chronic exposure to RNS are, in part, the result of persistent mitochondrial and nuclear DNA damage.

Nitric oxide donors induce large-scale deletion mutations in human lymphoblastoid cells: implications for mutations in T-lymphocytes from arthritis patients

Rheumatoid arthritis (RA) is an inflammatory disease in which high levels of reactive nitrogen oxygen species (RNOS) may be present in the affected joints. RNOS are known to produce small-scale mutational events (transitions, transversions, small insertions, and small deletions) but the ability of these compounds to cause deletion of large segments of genomic DNA has not been previously determined. To address this question, a human lymphoblastoid cell line (WIL2-NS) was exposed to nitric oxide (NO)-donating drugs and hypoxanthine phosphoribosyltransferase (hprt)-negative clones were selected and analyzed by multiplex-PCR. Large-scale deletions accounted for 60-80% of hprt mutations arising in drug-treated cultures compared to 12% in untreated cultures (P-values of 0.006 and 0.0001, respectively, in two experiments). Deletion mutations in untreated cultures affected exon 9, whereas 75% of drug-induced deletion mutations affected exons 2, 3, and 9, and the remainder were very large, ranging from 26 to 1200 kbp. To compare this spectrum of NO-induced mutations in a lymphoblastoid line to that arising in vivo in arthritis patients, T-cells from RA patients, osteoarthritis (OA) patients, and controls were cloned and similarly analyzed. We previously showed that the overall frequency of Hprt mutant clones from patients is appreciably elevated compared to that of control subjects. Large-scale hprt deletions (0.5 to >26 kb) were detected in mutant T-cell clones from both RA and OA patients and also from control subjects. A total of 54 mutant clones from 16 RA patients and 19 mutant clones from 6 OA patients were studied. Of these, 6 clones (from 3 RA and 1 OA patient) had suffered large-scale deletions. A total of 9 control subjects were studied and 62 mutant clones were obtained. Of these, 19 had suffered large-scale deletions, arising in 7 of 9 control subjects. In conclusion, (1) RNOS are capable of inducing large-scale deletion mutations in a human lymphoblastoid cell line and (2) large-scale deletion mutations were found in 10-30% of T-cell clones from RA and OA patients and controls, which we hypothesize may be induced by RNOS.

The role of uric acid in protection against peroxynitrite-mediated pathology

Peroxynitrite, the product of the free radicals nitric oxide and superoxide, has been implicated in the pathogenesis of inflammatory CNS disorders. Uric acid, an effective scavenger of peroxynitrite, is a purine metabolite present at high levels in the serum of hominoids relative to lower-order animals due to the functional deletion of urate oxidase. Raising the normally low levels of uric acid in mice is therapeutic for experimental allergic encephalomyelitis, an animal model of multiple sclerosis. This therapeutic activity of uric acid is associated with the inhibition of peroxynitrite-induced tissue damage, blood-CNS barrier permeability changes, and CNS inflammation. Based on these findings we have concluded that peroxynitrite has an important role in promoting enhanced vascular permeability and inflammatory cell extravasation. We hypothesize that higher uric acid levels in hominoids evolved to protect against this process.

Role of nitric oxide and superoxide in acute cardiac allograft rejection in rats

The role of NO and superoxide (O(2)(-)) in tissue injury during cardiac allograft rejection was investigated by using a rat ex vivo organ perfusion system. Excessive NO production and inducible NO synthase (iNOS) expression were observed in cardiac allografts at 5 days after cardiac transplantation, but not in cardiac isografts, as identified by electron spin resonance spectroscopy and Northern blotting. Cardiac isografts or allografts obtained on Day 5 after transplantation were perfused with Krebs bicarbonate buffer with or without various antidotes for NO or O(2)-, including N(omega)-monomethyl-L-arginine (L-NMMA; 1 mM), 2-phenyl-4,4,5, 5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO; 100 microM), 4-amino-6-hydroxypyrazolo[3,4-d]pyrimidine (AHPP; a xanthine oxidase inhibitor; 100 microM), and superoxide dismutase (SOD; 100 units/ml). Treatment of the cardiac allografts with PTIO showed most remarkable improvement of the cardiac injury as revealed by significant reduction in aspartate transaminase, lactate dehydrogenase, and creatine phosphokinase concentrations in the perfusate. Similar but less potent protective effect on the allograft injury was observed by treatment with L-NMMA, AHPP, and SOD. Immunohistochemical analyses for iNOS and nitrotyrosine indicated that iNOS is mainly expressed by macrophages infiltrating the allograft tissues, and nitrotyrosine formation was demonstrated not only in macrophages but also in cardiac myocytes of the allografts, providing indirect evidence for the generation of peroxynitrite during allograft rejection. Our results suggest that tissue injury in rat cardiac allografts during acute rejection is mediated by both NO and O(2)(-), possibly through peroxynitrite formation.

Depletion of intracellular glutathione reduces mutations by nitric oxide-donating drugs

The Mutatect system is a mouse tumor line in which mutations at the hypoxanthine phosphoribosyltransferase (Hprt) locus can be readily detected both in vitro and in vivo. We have previously shown that the nitric oxide-generating drugs, glyceryl trinitrate (GTN) and sodium nitroprusside (SNP), can induce mutations that are readily detected in these cells. In the present report, we have tested the effect of glutathione depletion by buthionine sulfoximine (BSO) on cytotoxicity and mutagenicity by these two drugs. Exposure for 24 h to either drug (123 microM GTN; 500 microM SNP) induced mutations with relatively little cytotoxicity. Pretreatment with 50 microM BSO for 24 h, and then removal at the time of GTN or SNP addition, enhanced cytotoxicity to a modest extent. However, mutagenicity induced by both GTN and SNP was largely abolished. BSO did not affect nitrite accumulation in the medium over a 24-h period, indicating no inhibition of bioactivation of GTN or SNP. Maintaining BSO in the medium for 24 h prior and throughout the period of exposure to GTN or SNP produced a similar effect on mutations. N-Acetylcysteine and oxothiazolidine-4-carboxylate, drugs that are used to increase intracellular glutathione, also blocked mutations. We postulate that a product of the reaction between nitric oxide and intracellular glutathione, such as GSNO or some species derived from it, is promutagenic.

Importance of guanine nitration and hydroxylation in DNA in vitro and in vivo

Guanine (Gua) modification by nitrating and hydroxylating systems was investigated in DNA. In isolated calf thymus DNA, 8-NO(2)-Gua and 8-oxo-Gua were dose-dependently formed with peroxynitrite, and 8-NO(2)-Gua was released in substantial amounts. Myeloperoxidase (MPO) with H(2)O(2) and NO(2)(-) reacted with calf thymus DNA to form 8-NO(2)-Gua dose dependently without release of 8-NO(2)-Gua. The frequency of strand breaks was higher than the sum of 8-NO(2)-Gua and 8-oxo-Gua, particularly in the MPO-treated DNA, indicating the importance of other types of damage. The activation of human neutrophils and lymphocytes with phorbol ester did not induce 8-NO(2)-Gua and 8-oxo-Gua in their nuclear DNA. However, 8-NO(2)-Gua was found in calf thymus DNA co-incubated with activated neutrophils in the presence of NO(2)(-). No significant formation of 8-NO(2)-Gua was found in liver DNA from mice treated with Escherichia coli lipopolysaccharide. The incubation of peroxynitrite or MPO-H(2)O(2)-NO(2)(-)-treated DNA with formamidopyrimidine glycosylase (Fpg) released 8-oxo-Gua, but not 8-NO(2)-Gua, indicating that 8-NO(2)-Gua is not a substrate for Fpg. Although 8-NO(2)-Gua was generated in isolated DNA by different nitrating systems, other types of damage were formed in abundance, and the lesion could not be found reliably in nuclear DNA, suggesting that the biological importance is limited.

Oxidation of ubiquinol by peroxynitrite: implications for protection of mitochondria against nitrosative damage

A major pathway of nitric oxide utilization in mitochondria is its conversion to peroxynitrite, a species involved in biomolecule damage via oxidation, hydroxylation and nitration reactions. In the present study the potential role of mitochondrial ubiquinol in protecting against peroxynitrite-mediated damage is examined and the requirements of the mitochondrial redox status that support this function of ubiquinol are established. (1) Absorption and EPR spectroscopy studies revealed that the reactions involved in the ubiquinol/peroxynitrite interaction were first-order in peroxynitrite and zero-order in ubiquinol, in agreement with the rate-limiting formation of a reactive intermediate formed during the isomerization of peroxynitrite to nitrate. Ubiquinol oxidation occurred in one-electron transfer steps as indicated by the formation of ubisemiquinone. (2) Peroxynitrite promoted, in a concentration-dependent manner, the formation of superoxide anion by mitochondrial membranes. (3) Ubiquinol protected against peroxynitrite-mediated nitration of tyrosine residues in albumin and mitochondrial membranes, as suggested by experimental models, entailing either addition of ubiquinol or expansion of the mitochondrial ubiquinol pool caused by selective inhibitors of complexes III and IV. (4) Increase in membrane-bound ubiquinol partially prevented the loss of mitochondrial respiratory function induced by peroxynitrite. These findings are analysed in terms of the redox transitions of ubiquinone linked to both nitrogen-centred radical scavenging and oxygen-centred radical production. It may be concluded that the reaction of mitochondrial ubiquinol with peroxynitrite is part of a complex regulatory mechanism with implications for mitochondrial function and integrity.

Apoptosis and the liver

Regulation of the homeostatic balance between cell proliferation and programmed cell death, apoptosis, is essential for development and maintenance of multicellular organisms. Apoptosis is a genetically and evolutionarily highly conserved process. Analysis of the molecular mechanisms of apoptosis has led to a better understanding of many human diseases. Notably in cancer, but also in infectious or autoimmune disease, a deficiency in apoptosis is one of the key events in pathophysiology. On the other hand, overefficient apoptosis, as observed in fulminant liver failure, may be equally harmful for the organism indicating that a tight regulation of the apoptotic machinery is essential for survival. The execution of apoptosis may be initiated by many different signals, either from within or outside the cell involving ligand-receptor interactions, as has been shown for Fas/Fas-ligand, TNF-alpha/TNF-receptor or TGF-beta/TGF-receptor, or potentially by more unspecific signals such as ceramide or DNA damage. During the modulation phase of apoptosis many different genes such as p53, c-myc or Bcl-2/Bax have been shown to able to shift the balance either to cell survival or cell death.

Selective involvement of superoxide anion, but not downstream compounds hydrogen peroxide and peroxynitrite, in tumor necrosis factor-alpha-induced apoptosis of rat mesangial cells

Tumor necrosis factor-alpha (TNF-alpha) induces reactive oxygen species (ROS) that serve as second messengers for intracellular signaling. Currently, precise roles of individual ROS in the actions of TNF-alpha remain to be elucidated. In this report, we investigated the roles of superoxide anion (O-(2)), hydrogen peroxide (H(2)O(2)), and peroxynitrite (ONOO(-)) in TNF-alpha-triggered apoptosis of mesangial cells. Mesangial cells stimulated by TNF-alpha produced O-(2) and underwent apoptosis. The apoptosis was inhibited by transfection with manganese superoxide dismutase or treatment with a pharmacological scavenger of O-(2), Tiron. In contrast, although exogenous H(2)O(2) induced apoptosis, TNF-alpha-triggered apoptosis was not affected either by transfection with catalase cDNA or by treatment with catalase protein or glutathione ethyl ester. Similarly, although ONOO(-) precursor SIN-1 induced apoptosis, treatment with a scavenger of ONOO(-), uric acid, or an inhibitor of nitric oxide synthesis, N(G)-nitro-L-argininemethyl ester hydrochloride, did not affect the TNF-alpha-triggered apoptosis. Like TNF-alpha-induced apoptosis, treatment with a O-(2)-releasing agent, pyrogallol, induced typical apoptosis even in the concurrent presence of scavengers for H(2)O(2) and ONOO(-). These results suggested that, in mesangial cells, TNF-alpha induces apoptosis through selective ROS. O-(2), but not H(2)O(2) or ONOO(-), was identified as the crucial mediator for the TNF-alpha-initiated, apoptotic pathway.

Biology of nitric oxide signaling

The free radical nitric oxide (NO) has emerged in recent years as a fundamental signaling molecule for the maintenance of homeostasis, as well as a potent cytotoxic effector involved in the pathogenesis of a wide range of human diseases. Although this paradoxical fate has generated confusion, separating the biological actions of NO on the basis of its physiologic chemistry provides a conceptual framework which helps to distinguish between the beneficial and toxic consequences of NO, and to envision potential therapeutic strategies for the future. Under normal conditions, NO produced in low concentration acts as a messenger and cytoprotective (antioxidant) factor, via direct interactions with transition metals and other free radicals. Alternatively, when the circumstances allow the formation of substantial amounts of NO and modify the cellular microenvironment (formation of the superoxide radical), the chemistry of NO will turn into indirect effects consecutive to the formation of dinitrogen trioxide and peroxynitrite. These "reactive nitrogen species" will, in turn, mediate both oxidative and nitrosative stresses, which form the basis of the cytotoxicity generally attributed to NO, relevant to the pathophysiology of inflammation, circulatory shock, and ischemia-reperfusion injury.

Peroxynitrite-mediated release of arachidonic acid from PC12 cells

A short term exposure of PC12 cells to a concentration of tert-butylhydroperoxide (tB-OOH) causing peroxynitrite-dependent DNA damage and cytotoxiticity promoted a release of arachidonic acid (AA) that was sensitive to phospholipase A(2) (PLA(2)) inhibitors and insensitive to phospholipase C or diacylglycerol lipase inhibitors. The extent of AA release was also mitigated by nitric oxide synthase (NOS) inhibitors and peroxynitrite scavengers. Low levels (10 microM) of authentic peroxynitrite restored the release of AA mediated by tB-OOH in NOS-inhibited cells whereas concentrations of peroxynitrite of 20 microM, or higher, effectively stimulated a PLA(2) inhibitor-sensitive release of AA also in the absence of additional treatments. These results are consistent with the possibility that endogenous as well as exogenous peroxynitrite promotes activation of PLA(2).

Expression of nitric oxide synthase-2 (NOS-2) in reactive astrocytes of the human glaucomatous optic nerve head

Inducible nitric oxide synthase (NOS-2) is abundantly present in the optic nerve heads of glaucoma patients. To determine the regulation of NOS-2 expression in the glaucomatous optic nerve head, the specific cells that express NOS-2 in the optic nerve heads of patients with primary open-angle glaucoma were studied by immunohistochemical double-labeling of NOS-2 and one of the characteristic cell markers for different cell types. Most of the labeling for NOS-2 was identified in reactive astrocytes that were clustered in the areas of nerve damage in the prelaminar and lamina cribrosa regions of the glaucomatous optic nerve heads. In vitro, the expression of GFAP and NOS-2 by reactive astrocytes of human optic nerve heads was demonstrated by immunocytochemistry and Western blot. In primary cultures of human lamina cribrosa astrocytes, stimulation by interferon-gamma and interleukin-1beta upregulated GFAP and induced expression of NOS-2 protein. At 24, 48 and 72 h of stimulation, NOS-2 appeared first in the Golgi body and then was sent out into the cytoplasm in granules. These results demonstrated that the astrocytes of human optic nerve head are capable of inducing the expression of NOS-2. Reactive astrocytes in the glaucomatous optic nerve heads apparently play an important role in local neurotoxicity to the axons of the retinal ganglion cells by producing excessive nitric oxide in glaucomatous optic neuropathy.

Endothelial dysfunction and peroxynitrite formation are early events in angiotensin-induced cardiovascular disorders

Angiotensin II (ANG II) is a well-established participant in many cardiovascular disorders, but the mechanisms involved are not clear. Vascular cell experiments suggest that ANG II is a potent stimulator of free radicals such as superoxide anion, an agent known to inactivate nitric oxide and promote the formation of peroxynitrite. Here we hypothesized that ANG II reduces the efficacy of NO-mediated vascular relaxation and promotes vascular peroxynitrite formation in vivo. ANG II was infused in rats at sub-pressor doses for 3 days. Systolic blood pressure and heart rate were unchanged on day 3 despite significant reductions in plasma renin activity. Thoracic aorta was isolated for functional and immunohistochemical evaluations. No difference in isolated vascular contractile responses to KCI (125 mM), phenylephrine, or ANG II was observed between groups. In contrast, relaxant response to acetylcholine (ACh) was decreased sixfold without a change in relaxant response to sodium nitroprusside. Extensive prevalence of 3-nitrotyrosine (3-NT, a stable biomarker of tissue peroxynitrite formation) immunoreactivity was observed in ANG II-treated vascular tissues and was specifically confined to the endothelium. Digital image analysis demonstrated a significant inverse correlation between ACh relaxant response and 3-NT immunoreactivity. These data demonstrate that ANG II selectively modifies vascular NO control at sub-pressor exposures in vivo. Thus, endothelial dysfunction apparently precedes other established ANG II-induced vascular pathologies, and this may be mediated by peroxynitrite formation in vivo. Wattanapitayakul, S., Weinstein, D. M., Holycross, B. J., Bauer, J. A. Endothelial dysfunction and peroxynitrite formation are early events in angiotensin-induced cardiovascular disorders.

NOX, a novel nitric oxide scavenger, reduces bacterial translocation in rats after endotoxin challenge

Endotoxemia promotes gut barrier failure and bacterial translocation (BT) by upregulating inducible nitric oxide synthase (iNOS) in the gut. We hypothesized that administration of a dithiocarbamate derivative, NOX, which scavenges nitric oxide (NO), may reduce intestinal injury and BT after lipopolysaccharide (LPS) challenge. Sprague-Dawley rats were randomized to receive NOX or normal saline via subcutaneously placed osmotic pumps before or after LPS challenge. Mesenteric lymph nodes, liver, spleen, and blood were cultured 24 h later. Transmucosal passage of Escherichia coli C-25 or fluorescent beads were measured in an Ussing chamber. Intestinal membranes were examined morphologically for apoptosis, iNOS expression, and nitrotyrosine immunoreactivity. NOX significantly reduced the incidence of bacteremia, BT, and transmucosal passage of bacteria and beads when administered before or up to 12 h after LPS challenge. LPS induced enterocyte apoptosis at the villus tips where bacterial entry was demonstrated by confocal microscopy. NOX significantly decreased the number of apoptotic nuclei and nitrotyrosine residues. NOX prevents LPS-induced gut barrier failure by scavenging NO and its toxic derivative, peroxynitrite.

Direct scavenging of nitric oxide by traditional crude drugs

Thirty-one traditional crude drugs and several pure compounds were examined for their possible regulatory effect on nitric oxide (NO) levels using sodium nitroprusside as a NO donor in vitro. Most of the crude drugs tested demonstrated direct scavenging of NO. Eight crude drugs, including Sanguisorbae Radix, Caryophylli Flos, Gambir, Coptidis Rhizoma, Granati Cortex, Gallae Rhois, Rhei Rhizoma and Cinnamomi Cortex exhibited significant activity (IC50 values < 1000 micrograms/ml), and with the exception of Coptidis Rhizoma, all were found to contain tannins as their major constituents. In addition, some crude drugs containing flavonoids or essential oils also appeared to act against NO. Ten major tannins contained in Sanguisorbae Radix and Rhei Rhizoma showed high scavenging activity (IC50 values < 326.3 micrograms/ml), and 6 of 8 alkaloids obtained from Coptidis Rhizoma also effectively scavenged the NO radical (IC50 values < 455.4 micrograms/ml). It was indicated that these compounds may be the active principles of the crude drugs responsible for NO scavenging. The present results suggest that traditional crude drugs might be potent and novel therapeutic agents for scavenging of NO and the regulation of pathological conditions caused by excessive NO and its oxidation product, peroxynitrite. These findings may also help to explain, at least in part, certain pharmacological activities of crude drugs, especially anti-infection and anti-inflammatory activities.

Dietary polyunsaturated fatty acids and cancers of the breast and colorectum: emerging evidence for their role as risk modifiers

The hypothesis that a high-fat diet promotes the development of postmenopausal breast cancer is supported by international data showing a strong correlation between fat intake and breast cancer rates and a modest positive association with high-fat diet in case-control studies. Dietary fat intake was found to be unrelated to the risk of breast cancer in cohort studies. In view of these conflicting findings it has been difficult to make nutritional recommendations for the prevention of breast cancer. Studies in animal models and recent observations in humans, however, have provided evidence that a high intake of omega-polyunsaturated fatty acids (PUFAs), stimulates several stages in the development of mammary and colon cancer, from an increase in oxidative DNA damage to effects on cell proliferation, free estrogen levels to hormonal catabolism. In contrast, fish oil-derived omega-3 fatty acids seem to prevent cancer by influencing the activity of enzymes and proteins related to intracellular signalling and, ultimately, cell proliferation. In this commentary, current evidence from experimental and human studies is summarized that implicates a high intake of omega-6 PUFAs in cancer of the breast, colon and, possibly, prostate and which indicates that omega-3 PUFAs and monounsaturated fatty acids such as oleic acid (omega-9) are protective. Plausible mechanisms for modulation of steps in the multistage carcinogenesis process by fats are discussed. Properly designed epidemiological studies are now needed, that integrate relevant biomarkers to unravel the contributions of different types of fat, their interactions with hormonal catabolism, protective nutritional factors and human cancer risk.

Peroxynitrite- and nitrite-induced oxidation of dopamine: implications for nitric oxide in dopaminergic cell loss

Increased nitric oxide (NO) production has been implicated in many examples of neuronal injury such as the selective neurotoxicity of methamphetamine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine to dopaminergic cells, presumably through the generation of the potent oxidant peroxynitrite (ONOO). Dopamine (DA) is a reactive molecule that, when oxidized to DA quinone, can bind to and inactivate proteins through the sulfhydryl group of the amino acid cysteine. In this study, we sought to determine if ONOO could oxidize DA and participate in this process of protein modification. We measured the oxidation of the catecholamine by following the binding of [3H]DA to the sulfhydryl-rich protein alcohol dehydrogenase. Results showed that ONOO oxidized DA in a concentration- and pH-dependent manner. We confirmed that the resulting DA-protein conjugates were predominantly 5-cysteinyl-DA residues. In addition, it was observed that ONOO decomposition products such as nitrite were also effective at oxidizing DA. These data suggest that the generation of NO and subsequent formation of ONOO or nitrite may contribute to the selective vulnerability of dopaminergic neurons through the oxidation of DA and modification of protein.